Cold air is bad for heart patients, especially when they are undertaking physical activity, because they are unable to cope with the higher oxygen demanded by the body.
"This study can help us understand why cold air is such a trigger for coronary events," said Lawrence I. Sinoway, professor of medicine and director of the Heart and Vascular Institute, Penn State College of Medicine.
Breathing cold air during exercise can cause uneven oxygen distribution throughout the heart. But a healthy body generally corrects for this problem and redistributes blood flow, making sure the heart continues to function properly.
In people with heart problems, such as coronary artery disease, this may not be the case, said Sinoway, the Journal of Applied Physiology and American Journal of Physiology, Heart and Circulatory Physiology report.
"If you are doing some type of isometric work and you're breathing cold air, your heart is doing more work -- it's consuming more oxygen," said Sinoway, according to Penn State statement.
Isometric work includes such activities as shovelling snow and carrying a briefcase or laptop bag. The heart works harder when exerted in cold temperatures and the number of deaths due to cardiac arrest peaks during the winter.
"There are two different things going on here -- demand and supply," said Matthew D. Muller, postdoctoral fellow at the Heart and Vascular Institute, Penn State College of Medicine.
"We thought that oxygen demand in the heart would be higher with cold-air breathing and we also thought that oxygen supply would be a little bit impaired. And that's generally what we found," added Muller.